This invention relates to an impedance matching device.
More particularly, the present invention relates to stripline used to form electronic impedance transformers on low temperature co-fired ceramics.
Impedance transformers, also known as impedance matching circuits, are used to connect circuits or devices of differing impedances in order to obtain maximum performance. For example, a power amplifier with an output impedance of 4xcexa9 would need an impedance transformer in order to get maximum power transferred to a 50xcexa9 antenna. With the proliferation of multi-mode, multi-band wireless systems and the advent of the software definable radio, broadband impedance transformers will play a crucial role in these systems. Without some form of broadband output matching network, multi-band radios would require a multiplicity of narrow, single band radio frequency (hereinafter referred to as RF) power amplifiers. However, single band RF power amplifiers are typically large in size and expensive to fabricate. Further, they tend to have large, unwanted inductive parasitics.
Tapered striplines with a constant ground plane spacing have been used as broadband impedance transformer, but have limited use due to the lengths of the striplines and the extreme line width ratio even for modest impedance ratios. The line width ratio is the width of the input divided by the width of the output. For example, a stripline (or line) that requires a 10 mil line width for a 50xcexa9 output would need a 350 mil stripline for a 4xcexa9 input, wherein the line width ratio is 1:35. In this case, the 4xcexa9 stripline requires a large package and in addition, makes for a complicated feed structure to a small surface mount component, such as a transistor.
Conversely, a stripline that requires a 40 mil stripline width for 4xcexa9 input would need a 0.65 mil stripline width for 50xcexa9 output, wherein the line width ratio is 1:61 (This assumes a stripline type transmission line, a dielectric constant of 7.8, and a dielectric height of 44 mils). In this case, the thin stripline for the 50xcexa9 output would significantly increase the loss of the transformer. Thus, if a stripline could be invented in which the ground plane spacing decreased along the length of the stripline, a transformer could be built in which the taper of the stripline could be reduced or eliminated.
It would be highly advantageous, therefore, to remedy the foregoing and other deficiencies inherent in the prior art.
To achieve the objects and advantages specified above and others, a new and improved impedance matching device is disclosed. The impedance matching device includes a ground plane, a stripline section positioned on the ground plane, the stripline section including N stripline regions wherein N is a whole number greater than or equal to one. Each stripline region includes a stripline sandwiched therebetween dielectric layers. Each adjacent stripline in the same section is connected in parallel wherein each adjacent stripline region is separated by a ground plane. Further, the thicknesses of the dielectric layers in at least one stripline section is greater than the thickness of the dielectric layers in an adjacent stripline section so that the distance between the stripline and the ground plane varies.
In the preferred embodiment, the striplines are tapered and the adjacent stripline within the same stripline section are electrically connected in parallel through conductive vias. A ground plane is positioned on the stripline region wherein a plurality of stripline sections are formed and electrically connected in series through conductive vias.